Interfacial tension is a property of the interface between two immiscible liquid phases and is analogous to surface tension at the interface between a liquid and a gas. It is thus a relative property of two liquids in contact. Interfacial tension can be defined as free energy per unit area of interface. Methods and devices for determining interfacial tension between two immiscible liquids are known. For instance, pendant drop methods, spinning drop methods. These methods are designed to exploit a balance between forces generated by the interface with gravity or centripetal acceleration respectively. Other methods utilize a probe, e.g., a plate or wire, that crosses the interface. In these methods, the force exerted by the interfacial tension on the probe is directly measured using a balance. A microfluidic sensor is disclosed in US20090019924 and another in US20110197664 (previously published in French as WO2009/125119). The latter relies on observation of the flow of one liquid within another and determines interfacial tension between the liquids from the flow rate at which the manner of flow changes from a jet to a stream of droplets. In this case the interfacial tension force is balanced by the viscous force introduced by the flow.